JPH01216047A - Method and device of controlling air-fuel ratio for engine - Google Patents

Abstract

PURPOSE:To improve air-fuel ratio control precision during transient running, by a method wherein, based on an detecting output for an exhaust gas compo nent, proportional computation and integrating computation are effected to perform feedback control of an air-fuel ratio, and according to a computing result of each computation, a learning factor is determined to correct an air-fuel ratio. CONSTITUTION:During running of an engine, a control circuit 60 computes a fundamental fuel injection time from an intake air amount and the number of revolutions of an engine, and by multiplying its result by a set air-fuel ratio factor, a fuel injection time is determined so that a target air-fuel ratio is obtained. By means of a feedback control amount by an exhaust gas sensor 142, a fuel injection amount is corrected to determine a final fuel injection time, by which an injector 12 is controlled. The feedback control amount is computed by means of a proportional gain, an integrating gain, and a differenti ating gain. In this case, from a computing result of the integrating gain, a steady learning factor is computed, and based on the learning factor, an air-fuel ratio is corrected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an engine air-fuel ratio control method and device;
In particular, the present invention relates to a control method and apparatus for feedback controlling the air-fuel ratio supplied to an engine based on exhaust gas components.

[Conventional technology]

For example, the mixture control of a general engine is disclosed in Japanese Patent Application Laid-open No. 58-25.
As disclosed in No. 540, the learning amount of the air-fuel ratio correction coefficient is determined from the feedback control amount based on the detected value of the exhaust gas component under a predetermined operating state of the engine.

As the capabilities of computers used for engine control and control systems including these computers improve, learning control is desired not only for specific operating conditions of the engine but also for a wider range of operating conditions.

[Problem to be solved by the invention]

In conventional air-fuel ratio feedback systems, only whether the air-fuel mixture is rich or lean is determined from the output of the exhaust gas sensor, and the air-fuel ratio of the air-fuel mixture is feedback-controlled based on this determination.

However, in this case, control is centered on the stoichiometric air-fuel ratio, and 5
There are problems with control accuracy and control responsiveness. Particularly in engine control, it is necessary to operate in a lean state or in a rich state other than the stoichiometric air-fuel ratio (λ; 1). It is difficult to adequately meet these demands with current feedback control systems.

An object of the present invention is to provide a feedback control method and device that can control the air-fuel mixture with high precision even in operating conditions other than the stoichiometric air-fuel ratio.

[Means to solve the problem]

One system for solving the above problem is an air-fuel ratio control method in which the exhaust gas components of the engine are detected and the air-fuel ratio of the mixture of fuel and air supplied to the engine is feedback-controlled based on the detected output. The feedback control is performed by performing proportional/integral calculation processing based on the gas detection output, and learning is performed based on the proportional calculation results and the integral calculation results, respectively.

[Effect]

In the present invention, proportional-integral feedback control is performed based on the deviation of the detected value of the exhaust gas component from the target value, and learning control is performed separately for the proportional component and the integral component.
Proportional component learning control can improve the control accuracy in transient engine operating conditions, and integral component learning control can improve control accuracy in the steady state of the engine.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

In order to comprehensively control the operating conditions of automobile gasoline engines, improve exhaust gas conditions, and improve fuel efficiency, a control device using a microcomputer captures signals from various sensors that indicate the engine's operating conditions. , performs various controls such as fuel supply amount and ignition timing,
2. Description of the Related Art Electronic engine control devices (hereinafter referred to as EECs) that enable optimal engine operating conditions have come into use.

An example of a system in which such EEC is applied to a fuel injection type internal combustion engine will be explained with reference to FIG.

Fig. 2 is a partial partial view schematically showing the entire engine control system, and the intake air is supplied to the air cleaner 2. Throttle chamber 4. It passes through the intake pipe 6 and is supplied to the cylinder 8. The gas burned in cylinder 8.

It passes through the exhaust pipe 10 and is discharged into the atmosphere.

The throttle chamber 4 is provided with an injector 12 for injecting fuel, and the fuel injected from the injector 12 is atomized within the air passage of the throttle chamber 4 and mixed with intake air to form an air-fuel mixture. Intake pipe 6
The air is supplied to the cylinder 8 by opening the intake valve 20.

The throttle valve 14 is configured to be mechanically interlocked with the accelerator pedal and is driven by the driver.

An air passage 22 is provided upstream of the throttle valve 14 of the throttle chamber 4, and a flow rate sensor 24 made of a thermal air flow meter made of an electric heating element is provided, and an electric signal AF that changes depending on the air flow velocity is provided. Output.

The injector 12 is constantly supplied with pressurized fuel from the fuel tank 30 via the fuel pump 32, and when an injection signal from the control circuit 60 is given to the injector 12, fuel is supplied from the injector 12 to the suction pipe 6. is injected.

The air-fuel mixture taken in from the intake valve 20 is compressed by the piston 50 and combusted by a spark from a spark plug (not shown) provided in each cylinder, and this combustion is converted into kinetic energy.

The cylinder 8 is cooled by cooling water 54. The temperature of this cooling water is measured by a water temperature sensor 56, and this measured value T
W is used as engine temperature.

An air-fuel ratio sensor (exhaust gas sensor) that outputs a signal based on or proportional to the air-fuel ratio A/F (Air Fuel Ratio) of the intake air-fuel mixture is attached to the collecting part 10 of the exhaust pipe of each cylinder.

In addition, a reference angle signal is generated on the crankshaft (not shown) at each reference crank angle, which is the process of each cylinder, according to the rotation of the engine, and a position signal is also output at each fixed angle (for example, 0.5 degrees). A crank angle sensor is provided.

The output of the crank angle sensor, the output signal TW of the water temperature sensor 56, the output signal of the exhaust gas sensor 142, and the electric signal AF from the air flow sensor enter a control circuit 60 consisting of a microcomputer.

It serves as an input to control the injector 12 and ignition circuit 62.

Further, the throttle chamber 4 is provided with a bypass 26 that communicates with the intake pipe 6 across the throttle valve 14, and this bypass 26 is provided with a bypass valve 61 that is controlled to open and close.

This bypass valve 61 is controlled to open and close by a pulse current, and its lift amount controls the cross-sectional area of the bypass 26, thereby controlling the amount of air supplied to the cylinder via the bypass 26.

EGR control Control 0 controls the passage between the exhaust pipe 10 and the suction pipe 6, and controls the amount of EGR from the exhaust pipe 10 to the suction pipe 6.

FIG. 3 is an overall configuration diagram of a control system using a microcomputer, which includes a central processing unit 102 (hereinafter referred to as CPU), a read-only memory 104 (hereinafter referred to as ROM), and a random access memory 106 (hereinafter referred to as ROM).
(hereinafter referred to as RAM) and the input/output circuit 108 are the control circuit 60
Configure.

The CPU 102 calculates a control value based on input data from the input/output circuit 108 using various programs stored in the ROM 104, and returns the calculation result to the input/output circuit 108 again. RAM 106 is used for intermediate storage necessary for these operations. CPU102. ROM10
Exchange of various data between the 4° RAM 106 and the input/output circuit 108 is performed by a path line 110 consisting of a data bus, a control bus, and an address bus.

The input/output circuit 108 inputs and outputs 1-bit information to a first analog-digital converter 122 (hereinafter referred to as ADC1), a second analog-digital converter 124 (hereinafter referred to as ADC2), and an angle signal processing circuit 126. Discrete input/output circuit 128 (hereinafter referred to as DIO) for
).

ADCl has a battery voltage detection sensor 132 (hereinafter referred to as VB
(hereinafter referred to as TWS) and cooling water temperature sensor 56 (hereinafter referred to as TWS)
The outputs of the air-fuel ratio sensor 142 (hereinafter referred to as A/FS) and the throttle sensor 14o (hereinafter referred to as 0TH8) are applied to the multiplexer 162 (hereinafter referred to as MPX), and the MPX 162 selects one of them. Select analog/digital conversion circuit 164 (hereinafter referred to as ADC)
Enter. The digital value that is the output of the ADC 164 is held in a register 166 (hereinafter referred to as REG).

In addition, the air flow sensor 24 (hereinafter referred to as AFS) is
The signal is input to C2.124, is digitally converted via an analog-to-digital converter ADC2.124 conversion circuit 172 (hereinafter referred to as ADC), and is set in a register 174 (hereinafter referred to as REG).

The angle sensor 146 (hereinafter referred to as ANGLS) outputs a signal (hereinafter referred to as REF) indicating a reference crank angle, for example 180 @ crank angle (in the case of 4 cylinders), and a minute angle, for example 0.
．． A signal indicating a 5-degree crank angle (hereinafter referred to as PO8) is output and applied to the angle signal processing circuit 126, where it is waveform-shaped.

DIO (128) has an idle switch 148 (hereinafter referred to as ID) that operates when the throttle valve 14 has returned to the fully closed position.
LE-3W) and top gear switch 150 (denoted as LE-3W)
(hereinafter referred to as TOP-8W) and starter switch 152
(hereinafter referred to as 5TART-5W) is input.

Next, a pulse output circuit and a controlled object based on the calculation results of the CPU will be explained. Injector control circuit 1134
(hereinafter referred to as INJC) is the digital value Ti of the calculation result
This is a circuit that converts the output into pulse output. Therefore, the pulse INJ having a pulse width corresponding to the fuel injection amount is INJC1
134 and applied to the injector 12 via an AND gate 1136.

Ignition pulse generation circuit 1138 (hereinafter referred to as IGNC)
has a register (hereinafter referred to as ADV) for setting a digital signal indicating the ignition timing and a register (hereinafter referred to as DWL) for setting the primary current energization start time of the ignition coil, and these data are set by the CPU. A pulse IGN is generated based on the set data and is applied via an AND gate 1140 to the ignition circuit 62 for supplying the primary current to the ignition coil.

The opening rate of the bypass valve 61 is controlled by the control circuit (hereinafter referred to as 15CC).
) 1142 through an AND gate 1144. l5CC
1142 has a register l5CD for setting the pulse width and a register l5CP for setting the pulse period.

The EGR amount control pulse generation circuit 1178 (hereinafter referred to as EGRC) that controls the EGR control valve 90 has a register EG'RD for setting a value representing a pulse duty and a register EGRP for setting a value representing a pulse period. are doing. This EGRC output pulse EGR is AN
is applied to transistor 90 via D-gate 1156.

Further, the 1-bit input/output signal is controlled by the circuit DIO (128). Input signals are IDLE-3W signal and 5TART-3W signal.

There is a TOP-3W signal. Further, the output signal includes a pulse output signal for opening the fuel pump. This D
The IO is provided with a register DDR192 for determining whether a terminal is used as an input terminal, and a register DOUT194 for latching output data.

The mode register 1160 is a register (hereinafter referred to as MOD) that holds instructions for commanding various states inside the input/output circuit 108.
For example, by setting an instruction in this mode register 1160, the AND gates 1136, 1
140,1144. .

All 1156 are activated or deactivated. By setting the command in the MOD register 1160 in this way, INJC and IGNC.

You can control the stop and start of rscc output.

A signal DIOI for controlling the fuel pump 32 is output to DIO (128).

Therefore, if such EEC is applied, almost all controls related to the internal combustion engine, such as air-fuel ratio control, can be appropriately performed, and the strict exhaust gas regulations for automobiles can be fully satisfied.

In the EEC shown in FIGS. 2 and 3, injector 1
The fuel injection according to No. 2 is performed in synchronization with the rotation of the engine, and the fuel injection amount is controlled by controlling the valve opening time of the injector 12 in one injection operation, that is, the fuel injection time Ti.

Therefore, in the embodiment of the present invention, this fuel injection time Ti is determined as follows.

T*”Krert” TR(1+β)-COEF+TS
...(1) TP=to-QA/N ...(2)
K vex: 1/λ・
...(3) Here, k: Coefficient determined by the injector QA: Intake air flow rate N: Engine speed TP: Basic fuel injection time β: Manipulated amount C0EF: Sum of various correction coefficients TS: Battery voltage correction time λ: Air Excess coefficient xrel: Set air-fuel ratio coefficient, that is, from intake air amount QA and engine rotation speed N (2)
The basic fuel injection time TP is calculated using the formula, multiplied by the set air-fuel ratio coefficient fuel injection time Ti
seek. Considering the dead time, time constant, and sampling period of the engine, it is preferable to calculate the manipulated variable β in synchronization with each engine rotation. Expressing the manipulated variable β using a difference equation, the following equation is obtained.

β=K P-e n+ΣKI-en +KD(an
-en -1)...(4) Here, KP is proportional gain and KI is integral gain.

KD is the differential gain g en is the current deviation g en 1
is the previous deviation. Furthermore, in the fourth equation above, KP·en is a proportional term βP, and ΣKI−en is an integral term βi.

K D (e n e n 1 ) is the differential term βd.

In this embodiment, using the manipulated variable β as a reference, learning control is performed to compensate for variations in characteristics of sensors, actuators, etc. and changes over time, and to improve driveability such as acceleration and deceleration, and emissions.

On a regular basis, large fluctuations in the manipulated variable β result in fluctuations in the air-fuel ratio due to overflow during calculation or changes in the set air-fuel ratio.
In a transient manner, the air-fuel ratio fluctuates due to fuel transport delays.

First, we will explain steady-state learning that compensates for variations in characteristics of sensors, actuators, etc. and changes over time. The exhaust gas sensor (A/F sensor) 142 generates an output proportional to the oxygen concentration in the exhaust gas.

Deviation e between the air-fuel ratio indicated by this exhaust gas sensor and the target air-fuel ratio
The manipulated variable β is calculated using equation (4) based on n, and the fuel injection time Ti is calculated using equation (1), the necessary amount of fuel is put into the cylinder, and feedback control is performed so that the target air-fuel ratio is achieved. With this manipulated variable β, the movement of the manipulated variable βi related to the integral term can be expressed as
As shown in the figure, when the manipulated variable βi exceeds the upper limit value (U, L) or is below the lower limit value (L, L), the deviation βC from zero is defined as the steady learning amount. This calculation of the steady learning amount βC is performed in all regions where feedback control by the exhaust gas sensor 142 is performed. Here, FIG. 5 shows a table in which the steady learning amount βC is written. In this table, βC is written in the interval determined by the basic fuel injection time TP and the engine rotational speed N. The timing of this learning is when the dividing point does not change and the operation amount β
This is performed when i is outside the range of the upper and lower limits. Here, upper and lower limits are provided, but learning can be performed even if the upper and lower limits are eliminated. In this case, the table in FIG. 5 is rewritten with the deviation βC from the target value (zero here), regardless of whether the manipulated variable βi exceeds the upper or lower limit values. Although learning is performed for each divided area as shown in FIG. 5, it takes a very long time to learn over the entire area of the steady learning map. Therefore, it is necessary to create unlearned divided regions with reference to the learned region.

This creation method will be explained.

FIG. 6 shows the configuration of a buffer map and a comparison map having the same number of regions as the divided regions of the steady learning map for creating the steady learning map.

FIG. 7 shows a block diagram of the learning map creation routine.

In equation (1), the steady learning map and comparison map are all cleared, and the learning amount is written to the buffer map. However, at this point, double writing to the buffer map is not performed. When the number of writes to the buffer map reaches C in (2), transfer the contents of the buffer map to the comparison map, and refer to the C contents written to the buffer map in (3) to Create a learning area and transfer its contents to the learning map.

In (4), the contents of the comparison map are retransferred to the buffer map. From this point on, the value of the learning amount βC of the steady learning map is used to calculate the fuel injection time. From (5) onwards, the learned values are written into both the steady learning map and the buffer map, and the contents of the buffer map and comparison map are compared. When the difference in the compared contents reaches a certain number, (6) ~
In (8), perform the same work as in (2) to (4). Here, C is, for example, 1, and in the case of 1, there may be a special learning value, so the value is half of the learning value βC. Weighting is performed such that the learning value is set as the learning value. Also, if C is 2,
Let the value of 3/4 of the learning value βC be the learning value. When C is 3 or more, the learned value βC itself is used as the learned value.

Here, explanation is given using a steady learning map, a buffer map, and a comparison map, but it is also possible to use only a steady learning map and make the division points coarser so that constant learning is performed.

Next, an example of a learning routine for the steady learning coefficient (learning amount) βC will be described with reference to FIG. The process according to this flowchart is repeated at a predetermined cycle from step 300 to step 338 after the engine is started. First, in step 302, it is determined whether air-fuel ratio feedback control is on, and if the result is Yes, the process proceeds to step 304. If the result is No, proceed to step 338.

In step 304, the manipulated variable βi is checked,
If it is outside the range of the upper and lower limit values, proceed to step 306,
If it is within the range, the process advances to step 336. Step 306
Now, the learning value βC is calculated. That is, since the manipulated variable βi is the manipulated variable of the code material, the manipulated variable βi itself becomes the steady learning βC.

In step 316, division points of the learning map are calculated from the rotation axis of the engine speed and the load axis of the fuel injection time shown in FIG. In step 318, it is checked whether the current dividing point has changed from the dividing point calculated -period ago. If the 0 dividing point has not changed, the counter is incremented in step 320. In step 322, when the counter reaches n, in step 324, the value of the dividing point of the buffer map is added to βC, and the limiter is checked. If the learning map is being created in step 326, step 336
If 0 is not being created, a check is made in step 328 to see if the first learning map creation is complete. If it is completed, the learning value βC is stored in the learning map in step 330, and the integral term is set to zero. As a result, the operation amount βi shown in FIG. 4 moves around zero. If the creation of the first learning map has not been completed, step 332 indicates that the divided areas of the buffer map have already been learned, do not double write and proceed to step 336; if not, step 334 Learning value βC on map
is stored, and the counter is cleared in step 334.

In this way, in the fuel control system for gasoline engines, etc., it is possible to always maintain the optimal air-fuel ratio without the need for special adjustments, especially in response to variations in the characteristics of fuel control system sensors, actuators, etc. and changes over time. Can be done.

Next, the learning map creation routine explained in FIG. 7 will be explained with reference to the flowchart in FIG.

At step 350, it is determined whether the first learning map has been created. If it has not yet been created, proceed to step 354;
Check the number of buffer map writes. Add weight according to the number of learning items from 1 to 3 and proceed to step 35.
6, but if no learning is being performed, the process proceeds to step 370. If the first learning map is created in step 350, the difference in data between the buffer map and the comparison map is checked in step 352. If there are Q differences in content between the buffer map and the comparison map, step 356
Proceed to step 2 and create a steady learning map. Q about the content
If there is no difference, proceed to step 370.

At step 356, a map creation flag is set;
Prohibit writing learning results. In step 358, the contents of the buffer map are transferred to the comparison map, and step 3
At 60, a steady learning map is created using the buffer map. In step 362, the contents of the created buffer map are transferred to the learning map, and in step 364, the contents of the comparison map and the buffer map are transferred to the learning map. At step 366, a flag indicating that the learning map has been created is set. This flag is used for the determination in step 350. In step 368, the settings were made in step 356.

Reset the map creation flag.

Next, FIG. 10 shows the relationship between the basic fuel injection time tp and the manipulated variable βp related to the proportional term in a transient state.

Changes in the transient state can be determined by the amount of change Δ'rp in the basic fuel injection time tp, as shown in FIG. 10(1). During the acceleration period when this ΔTp is increasing and the deceleration period when it is decreasing, the manipulated variable β
p indicates the extreme values a and b, and these extreme values a and b are the upper limit values (
K, U, L) or below the lower limit (K, L, L), the acceleration learning amount βa or deceleration learning amount βd is set.

Figures 11 and 12 show an acceleration learning map and a deceleration learning map. These maps are made up of the basic fuel injection time change ΔTp and the engine rotational speed N, and the acceleration and deceleration period per hour. A dividing point is calculated from the engine speed N at the time when the maximum change amount ΔTp is detected, and learned values βa and βd at subsequent extreme values are written in each map.

FIG. 1 describes an example of transient learning using a flowchart.

In step 400, it is also checked whether the learning map is allowed to be used, and if the use is prohibited, the process proceeds to step 424, and if the use is allowed, the process proceeds to step 402.

Check the air-fuel ratio feedback control, and if it is under control, go to step 404; if not, go to step 42
4. In step 404, it is checked whether an acceleration or deceleration learning map is being created, and if it is being created, step 424 is performed.
If it is not being created, proceed to step 406. In step 406, the acceleration or deceleration state is checked. If the acceleration or deceleration is in progress, proceed to step 408. If the acceleration or deceleration is not in progress, proceed to step 424. Here, the acceleration or deceleration state is checked. The determination is made by comparing the change Δtp in the basic fuel injection time with a predetermined value.
In step 408, it is determined whether the manipulated variable β is within upper and lower limit values (KUL, KLL) shown in FIG. If it is within the upper and lower limits, proceed to step 424 and the result is N.
If O, the process proceeds to step 410. In step 410, the manipulated variable βp is set as the transient learning amount.

In step 416, a dividing point is calculated from the engine rotational speed N at the time when acceleration/deceleration is detected and the change ΔTp in the basic fuel injection time at that time. In step 418, it is determined whether the detected acceleration or deceleration is acceleration or deceleration. If acceleration, the acceleration learning value βp is added to the acceleration learning map in step 420, and if it is deceleration, the deceleration learning value βp is added to the deceleration learning map in step 422. Add the value βd.

Here, the transient learning map is explained as one acceleration learning map and one deceleration learning map, but depending on the size of the load, having two to three maps allows for more precise air-fuel ratio control. .

The above steady learning and transient learning were included. Fuel injection time T
From equation (1), i is as follows.

T i =KrecT P (1+β+βC+βdyn
) COEF+TS...(4) Here, βC: Steady learning value βdyn: Transient learning value Transient learning value βdyn is acceleration learning value βa or deceleration learning value β
d, but only the steady learning value βC is used in the steady operating state of the engine.

In this embodiment, the learning amount is the manipulation amount of the code material itself, but even if it is a difference from a certain limit value, the learning effect will not change in any way.

Next, another embodiment of the present invention will be described using the drawings.

First, the fuel supply amount is calculated using the first to third equations.

In equations 1 to 3, proportional, integral,
It is desirable to perform precise air-fuel ratio control using differential operation.
Therefore, in consideration of the dead time, time constant, and sampling period of the engine, it is preferable to calculate the manipulated variable β using a microcomputer in synchronization with the engine rotation.

When this manipulated variable β is expressed by a difference equation, it becomes the following equation.

β=Kp-e+ΣKi-e+Kd・(e-1)-(4)
Here, Kp: proportional gain Ki: integral gain e: deviation (e-1): difference value of the current deviation with respect to the deviation one time before.
When controlling the fuel injection time Ti (fuel injection amount) using the ID control law, the air-fuel ratio is extracted for each cylinder in rotational synchronization with the output of the air-fuel ratio sensor to eliminate variations in the air-fuel ratio between each cylinder. Fuel injection is performed with this in mind, and the air-fuel ratio is made uniform for each cylinder. First, in order to show the characteristics of the air-fuel ratio sensor, FIG. 13 shows a characteristic diagram of a linear air-fuel ratio sensor and an output characteristic diagram with respect to changes in the air-fuel ratio. The output voltage of the sensor is the 13th with respect to the excess air ratio, which is the ratio of the air-fuel ratio to the stoichiometric air-fuel ratio.
As shown in the figure, since it is obtained as a continuous value, variations in the output voltage of the sensor can be obtained for each minute variation in the air-fuel ratio of rich, lean, and stoichiometric air-fuel ratios. On the other hand, in the case of the conventionally used oxygen sensor shown in Fig. 14, which has digital output characteristics near the stoichiometric air-fuel ratio, the output voltage changes greatly near the stoichiometric air-fuel ratio in response to minute fluctuations in the air-fuel ratio. Since the output characteristics are constant in the lean and rich regions, fluctuations in the air-fuel ratio cannot be detected.

Due to the above-mentioned physical characteristics, it is possible to detect fluctuations in the air-fuel ratio by using a linear air-fuel ratio sensor, and since the sensor has a fast response speed, it is possible to detect changes in the air-fuel ratio for each cylinder. Fig. 16 shows a chart for taking in the air-fuel ratio for each cylinder, and Fig. 15 shows the signal processing flow. In this embodiment, the air-fuel ratio of each cylinder is detected in synchronization with the rotation, and Performs fuel injection control.

When entering the rotation synchronization task 500 in FIG.
First, in step '510, the air-fuel ratios for each cylinder are captured in rotational synchronization.In step 512, the average air-fuel ratio of all cylinders is calculated using the latest air-fuel ratios of the remaining cylinders. In step 514, this all-cylinder average air-fuel ratio is used to calculate proportional, integral,
The operation control amount of the differential control law is calculated, and in step 516, the cylinder-specific air-fuel ratio correction coefficient for the 0th next fuel injection, which is set as the basic operation control amount in the main air-fuel ratio control, is calculated based on the engine rotation speed N, the engine load Tp, and the next fuel injection. The 0th fuel injection time Ti to be searched for the cylinder corresponding to the injection is calculated in step 518 using the coefficients obtained in these processes.Then, in step 520, the stationarity of the engine operating state is determined. Steady state is a state in which the engine is rotating stably, rather than in a state of acceleration or deceleration. If it is steady, the cylinder-specific air-fuel ratio correction coefficient is learned. Prior to this process, the deviation of the air-fuel ratio for each cylinder from the average air-fuel ratio is calculated in step 522.
In step 524, a cylinder-by-cylinder air-fuel ratio correction coefficient is calculated based on the deviation from the average air-fuel ratio, and in step 526, a cylinder-by-cylinder air-fuel ratio correction coefficient map is calculated for engine speed N and load 'rp in a steady state. Updating and calculating the correction coefficient for each cylinder air-fuel ratio in step 518 in the process of 0 or more in preparation for the next search is performed in the rotation synchronization process, and the subsequent processes from steps 520 to 526 are performed by other processes. This may be done with lower priority tasks.

FIG. 16 shows a time chart of the intake of air-fuel ratio by cylinder and the stroke of each cylinder. Here, the case of 4 cylinders will be explained as an example. REF in FIG. 16(a) is a cylinder signal, and in particular, in this case, the cylinder signal corresponding to the ignition timing of the first cylinder has a wide pulse width and is used as a cylinder discrimination signal. The strokes of the first cylinder and other cylinders are shown in Figure 16 (c).
, (ho).

As shown in (f) and (g), the corresponding cylinders of the exhaust gas detected by the air-fuel ratio sensor with linear characteristics installed in the exhaust gas collecting section are as shown in (4). For example, the cylinder If the air-fuel ratio is taken in at the rising edge of the discrimination signal,
This is the air-fuel ratio of the fourth cylinder.

Similarly, if the next cylinder signal is captured in synchronization with the rising edge of the signal (su), the cylinder of that captured signal will be the second cylinder.
cylinder, then the first cylinder, and then the third cylinder. Further, the cylinder-specific correction coefficient calculated by rotation synchronization processing at the rise of the cylinder discrimination signal is reflected in the fuel injection of the second cylinder. By performing fuel injection for each cylinder by matching the order of these processes, air-fuel ratio control for each cylinder can be performed.

FIG. 17 is a detailed time chart of fuel injection amount control for each cylinder based on the above timing chart and FIG. 15 is a schematic flowchart of fuel injection amount control. When entering the rotation synchronization task 500, first in step 532 the cylinder signal REF is input.
Enter the count value. At the start of cylinder discrimination, this count value is reset to ``0'', that is, 1''0''.

It takes four values “1”, '2”, and 3”, and each
0, which is the identification number corresponding to the ignition of the cylinder, 3rd cylinder, 4th cylinder, and 2nd cylinder. Next, in step 534, the air-fuel ratio for each rotationally synchronized cylinder is captured, and the cylinder identification number of the captured air-fuel ratio is used in step 534. At 536, it is calculated and stored.

Next, in step 538, the average air-fuel ratio of all cylinders is calculated from the air-fuel ratio of each cylinder taken in so far. Using this all-cylinder average air-fuel ratio, the basic operation control amount is calculated in step 540. At this time, the basic operation control amount is calculated using the proportional, integral, and differential control law shown in equation 4. Furthermore, the correction coefficient of the air-fuel ratio for each cylinder for the next fuel injection amount is determined in step 542.
First, calculate the identification number of the target cylinder, search for the correction coefficient using the engine rotation speed N, load 'rp, and the cylinder identification number, and set the result. The fuel injection amount is calculated using the obtained cylinder-by-cylinder air-fuel ratio correction coefficient and the basic operation control amount calculated in step 540. The basic calculation formula is based on equation (1), and the feature here is that the sum of the basic operation control amount and the air-fuel ratio correction coefficient for each cylinder is used as the operation control amount.

Next, learning of the air-fuel ratio correction coefficient for each cylinder will be described below. First, for stationarity evaluation, if the deviation from the average of the average engine speed and load at M points in the past is smaller than a predetermined value, it is assumed to be stationary, and if it is stationary, step 548
In step 550, the cylinder specific deviation in the steady range of each cylinder is calculated.
Calculate for each cylinder. Using these values, the cylinder-by-cylinder air-fuel ratio correction coefficient map is updated in step 552. At this time, a constant multiple of the cylinder-specific deviation is added to the previous value of the cylinder-specific air-fuel ratio correction coefficient to obtain a new cylinder-specific air-fuel ratio correction coefficient.

This completes this process. The timing chart of the operation as a result of the above processing is shown in Fig. 18. At the rise of the cylinder discrimination signal, the read air-fuel ratio of the fourth cylinder is used to calculate the signal for the three cylinders ahead, and then Fuel is injected at the timing of the signal and sucked into the fourth cylinder during the next intake stroke. FIG. 19 shows the configuration of the air-fuel ratio correction coefficient map for each cylinder. In this case, the engine speed and the load are each divided into eight parts, and each cylinder has an air-fuel ratio correction coefficient for each operating region. Since each cylinder has a map, it becomes a four-sided map. FIG. 20 shows an example of the output of the linear air-fuel ratio sensor when this embodiment is used. The ring below the eye shows how the output signal, which has a lot of ripple due to variations in the air-fuel ratio of each cylinder, gradually becomes less ripple and the air-fuel ratio of each cylinder becomes even. After learning, a more uniform air-fuel ratio can be achieved than at the beginning. Furthermore, when the set air-fuel ratio is changed and a new air-fuel ratio is reached, since no learning has been done, there will initially be variations in the air-fuel ratio between cylinders, and then the ripple will gradually increase due to the effect of learning the air-fuel ratio correction coefficient for each cylinder. This results in an air-fuel ratio output with less variation across all cylinders.

According to the above embodiment, since there is a map of air-fuel ratio correction coefficients for each cylinder according to the operating conditions, it is possible to realize engine operation in which the air-fuel ratio among the cylinders is uniform under all operating conditions. Can be made larger and reduce fuel consumption.
In addition, since the air-fuel ratio is uniform, there is little rotational fluctuation, so there is an effect that the engine can be controlled with little rotational fluctuation and surge, especially when idling or at low rotational speeds.

In this embodiment, the cylinder-by-cylinder air-fuel ratio correction coefficient has a memory for each engine speed and load, rather than a map, and is effective even when cylinder-by-cylinder fuel correction is performed. This has the effect of making fuel correction possible.

In the embodiment of the present invention, as the characteristics shown in FIG. 13 suggest, there is no perfect linearity, so when calculating the excess air ratio (air-fuel ratio), it is necessary to calculate using a polygonal line approximation. Therefore, it would have been desirable to have an air-fuel ratio correction coefficient map for each cylinder based on engine speed, load, etc. However, by using an air-fuel ratio sensor with sufficient linearity, the excess air ratio (air-fuel ratio) can be detected in real time, and the air-fuel ratio value between the cylinders can be directly obtained. Since the fuel adhering to the wall surface can be calculated from the resulting air-fuel ratio, the rotational speed of the map and the number of load divisions can be reduced, and accurate cylinder-by-cylinder air-fuel ratio control can be realized with a small memory capacity.

Figure 21 shows the flow of calculating the air-fuel ratio correction coefficient for each cylinder.
According to this embodiment, since accurate fuel adhesion can be calculated,
This has the effect of realizing engine control with better controllability (the time required to achieve uniformity can be shortened).

According to the present invention, cylinder-by-cylinder air-fuel ratio control is performed to smooth the air-fuel ratio for each cylinder, so there is no variation between cylinders due to fuel adhesion to the wall surface of each cylinder, and roughness at idle can be reduced. Also, in lean combustion, the lean limit can be expanded because the air-fuel ratio among the cylinders becomes uniform.

Still other embodiments are shown in FIGS. 22 and 23.

When the rotation synchronization interrupt process 570 is entered in FIG. 22, the air-fuel ratio for each cylinder is captured in step 572. Next, in step 574, the average air-fuel ratio of all cylinders is calculated using the latest air-fuel ratio of each cylinder. Using this all-cylinder average air-fuel ratio, the manipulated variable β of the proportional/integral/derivative control law is calculated in step 576.

This is the basic manipulated variable in this air-fuel ratio control. Next, in step 578, a phase counter is set based on the engine speed N and the load Tp. This is a zero-order process that takes into consideration factors such as transportation delay of injected fuel, fuel adhesion, overlap of intake and exhaust valves, and the length from the exhaust valve to the exhaust gas collecting part where the air-fuel ratio sensor is installed. Next, the cylinder-by-cylinder air-fuel ratio correction coefficient for the current fuel injection is searched for in step 580, and the current fuel injection time Ti is calculated by the first equation using the coefficients obtained in the above processing. This result is set in the pulse generation circuit 1134 in step 582.

FIG. 33 shows a schematic flowchart of the cylinder-by-cylinder air-fuel ratio correction coefficient calculation performed in a low-priority task. When entering task 600, it is determined in step 602 whether or not fuel is being cut, and in step 604 it is checked whether the vehicle is in an acceleration/deceleration state.

When neither is the case, the deviation between the average air-fuel ratio and the air-fuel ratio of each cylinder, which is processed by rotation interrupt, is calculated in step 606, and the air-fuel ratio correction coefficient for each cylinder is calculated in step 608. Fuel cut and acceleration/deceleration are performed. In this state, the air-fuel ratio for each cylinder is changing from moment to moment, so the correction coefficient is not calculated.However, when calculating the fuel for each cylinder, there is no need to use the air-fuel ratio correction coefficient for each cylinder before the change. No problem.

According to this embodiment, since the cylinder-specific air-fuel ratio correction coefficient is selectively used even when the throttle opening is 40'' or more, where the air-fuel ratio fluctuation between cylinders becomes large, the air-fuel ratio correction coefficient between cylinders is The fuel ratio can be made uniform. Therefore, torque fluctuations are reduced, and rotational fluctuations are also reduced thereby, making it possible to lower idling speeds in particular. Also, in the power range, changes in charging efficiency due to rotational fluctuations can be achieved. This has the effect of maximizing control over engine performance.

According to the embodiment of the present invention, the phase counter is determined based on the engine speed and load, but factors such as fuel transport delay, fuel adhesion, overlap of intake and exhaust valves, and length of exhaust gas collecting section are determined based on engine speed and load. It varies depending on temperature and other conditions. or,
Since it varies depending on the type of car, if you set upper and lower limiters for the deviation in the deviation calculation 420, and when the limiter is exceeded, the phase counter is accelerated or delayed so that it enters the limiter. This has the effect of enabling auto-tuning to equalize the air-fuel ratio for each cylinder.

Although the calculation in FIG. 23 is performed by a low-priority task, it may also be performed by the rotation interrupt shown in FIG. 22. Then, step 57 calculates the average air-fuel ratio for all cylinders.
Although this is performed every rotation interruption as shown in 4, if the average air-fuel ratio is calculated after taking in the number of cylinders from the reference cylinder, control accuracy will be improved. At this time, steps 606 and 608
Of course, this should be done only when the average air-fuel ratio has been calculated.

Furthermore, if the air-fuel ratio reading and memory for each cylinder is carried out over several cycles, it is possible to calculate the air-fuel ratio correction coefficient for each cylinder, taking into account fluctuations in the rotational speed.

According to this embodiment, cylinder-by-cylinder air-fuel ratio control is performed to smooth the air-fuel ratio for each cylinder, eliminating variations in fuel distribution for each cylinder and fuel adhesion to the wall, reducing roughness during idling. This allows for automatic tuning. Furthermore, in lean combustion, the lean flammability limit can be expanded because the air-fuel ratio among the cylinders can be made uniform. And since the air-fuel ratio between cylinders can be controlled, proportional, integral,
Each gain of the differential can be increased, and the controllability of the air-fuel ratio can be improved. This has the effect of reducing torque fluctuations, reducing vibration, and improving riding comfort.

〔Effect of the invention〕

According to the present invention, it is possible not only to compensate for variations in characteristics and changes over time of sensors and actuators related to air-fuel ratio control, but also to control the air-fuel ratio by acceleration and deceleration with high precision.

[Brief explanation of the drawing]

Fig. 1 is a flowchart showing an example of transient learning, Fig. 2 is a schematic diagram showing an example of an electronic engine control device, Fig. 3 is a block diagram showing a control system, and Fig. 4 is a manipulated variable in steady-state learning. An explanatory diagram of the operation of βi, Fig. 5 is a configuration diagram of a steady learning map, Fig. 6 is a diagram of the arrangement of steady learning, buffer and comparison maps, Fig. 7 is an explanatory diagram of the creation status of each map, and Fig. 8 is a diagram of the steady learning map. Figure 9 is a flowchart showing the amount of learning, Figure 9 is a flowchart for creating a steady learning map, Figure 10 is an explanatory diagram explaining acceleration/deceleration learning operation, Figures 11 and 12 are configuration diagrams of acceleration/deceleration learning map, Figure Figure 13 is a characteristic diagram of a linear air-fuel ratio sensor and an output characteristic diagram with respect to air-fuel ratio changes, Figure 14 is a characteristic diagram of an oxygen sensor and an output characteristic diagram with respect to air-fuel ratio changes, and Figure 15 is a schematic flow of fuel injection amount control. figure,
Fig. 16 is a time chart of cylinder-specific air-fuel ratio intake and stroke of each cylinder, Fig. 17 is a flow diagram of cylinder-specific fuel injection amount control, and Fig. 18 is a detailed time chart of cylinder-specific fuel injection amount control. Fig. 19 is a configuration diagram of a cylinder-specific air-fuel ratio deviation map, Fig. 20 is a time chart of a control example, Fig. 21 is a flowchart of calculating a cylinder-specific air-fuel ratio correction coefficient using an air-fuel ratio sensor with good linearity, FIG. 22 is a flowchart of cylinder-specific fuel injection control using rotation synchronization interrupt processing, No. 23.
The figure is a flowchart for calculating air-fuel ratio correction coefficients for each cylinder. 12... Injector, 24... Air flow sensor,
60...Control circuit, 106...RAM, 142...
- Air-fuel ratio sensor, 1134... Injector control circuit. No. I G No. 2 312] Tea 5 Showa 7th Daqri: J Fig. 13 #150 185P1i-Gang No. 210

Claims (1)

[Claims] 1. In an air-fuel ratio control method that detects engine exhaust gas components and feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the engine based on the detection output, proportional calculation is performed based on the exhaust gas detection output. and performing integral calculations to perform the above-mentioned feedback control, and to obtain respective learning coefficients based on each of the above-mentioned proportional calculation results and the above-mentioned integral calculation results, and correct the air-fuel ratio of the air-fuel mixture using these learning coefficients. Characteristic engine air-fuel ratio control method. 2. In an air-fuel ratio control method that detects engine exhaust gas components and feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the engine based on this detection result, a feedback coefficient is determined based on the deviation between the detection result and its target value. In addition to computing the proportional and integral components of , a transient learning coefficient for the transient operating state of the engine is computed from the computing result of the proportional component, and a steady learning coefficient for the steady operating state of the engine is computed from the computing result of the integral. A method for controlling an engine air-fuel ratio, characterized in that the air-fuel ratio of the air-fuel mixture is corrected using the feedback coefficient and the learning coefficient. 3. In an engine control method that detects engine exhaust gas components and feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the engine based on the detection results, the detection results are detected for each cylinder of the engine, and the Based on the difference between the detection result for each cylinder and a predetermined target value, a cylinder correction coefficient corresponding to each cylinder is calculated to eliminate variations between each cylinder, and this cylinder correction coefficient is used to adjust the air-fuel mixture for each cylinder. An air-fuel ratio control method for an engine, the method comprising controlling a fuel ratio. 4. In an engine control method that detects exhaust gas components of the engine and feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the engine based on the detection result, detecting the exhaust gas components corresponding to each cylinder, Calculate the average air-fuel ratio of the cylinders from the above detection results, calculate the cylinder correction coefficient for each cylinder based on the above average air-fuel ratio and the air-fuel ratio corresponding to each cylinder, and calculate the cylinder correction coefficient for each cylinder based on this cylinder correction coefficient. 1. A method for controlling an air-fuel ratio of an engine, the method comprising: controlling the air-fuel ratio of a mixture. 5. An exhaust gas sensor for detecting exhaust gas components is provided at the exhaust gas collection point of each cylinder of the engine, and the state of the air-fuel ratio corresponding to each cylinder is detected from the output of the exhaust gas sensor in synchronization with the rotation of the engine. means for feeding back the air-fuel ratio by performing proportional calculation and integral calculation for each cylinder based on the state of the air-fuel ratio corresponding to each cylinder and the target air-fuel ratio, and calculating a steady-state learning value from the result of the integral calculation. What is claimed is: 1. An air-fuel ratio control device for an engine, comprising: means for determining the constant learning value; and means for further correcting the air-fuel ratio based on the steady-state learning value.